Several types of antihistamines are available over the counter and are used to relieve symptoms of hay fever and allergies. They work by blocking the effects of histamine in the body. Histamine causes itching, sneezing, runny nose, watery eyes and can cause difficulty breathing. There are first generation antihistamines that affect the H1 receptor in the body, second generation antihistamines that affect the H2 receptors, and new experimental medications that affect the recently discovered H3 and H4 receptors.
Treating Allergies
The primary use of antihistamine medications is to treat allergic reactions. According to the American Academy of Otolaryngology, antihistamines work best when they are taken before the symptoms of allergies are fully established. They work to block histamine in the body by attaching to the receptors where the histamine would normally go. They do not cure the allergic reaction, but do provide relief for some of the discomforts caused by seasonal allergies.
Sleepiness
First generation antihistamines block the H1 receptors in the body. According to FamilyDoctor.org, these medications can make you sleepy and will affect the ability to drive or operate heavy machinery. The first generation medications can make it difficult to think clearly. The second generation antihistamines that affect the H2 receptors, however, are much less likely to cause this side effect.
Treating Motion Sickness
According to FamilyDoctor.org, first generation antihistamines will work on the part of the brain that affects nausea and vomiting. The medication blocks these symptoms and is an effective preventative treatment for motion sickness caused by boat rides and car rides.
Dry Membranes
Antihistamines are designed to dry up a runny nose and watery eyes. However, they can also have the effect of drying out membranes in the nose, mouth and throat, according to physicians at Mayo Clinic. When the membranes dry out, the mucus in the nose and throat may also thicken as a secondary effect. While this may not have much of an effect on adults, it can cause the mucus in the inner ear to thicken and increase the risk of ear infections in young children.
